Competitive Bonding of Amino and Hydroxyl Groups in Ethanolamine on Si(100)2×1: Temperature-Dependent X-Ray Photoemission and Thermal Desorption Studies of Nanochemistry of a Double-Chelating Agent
Temperature-dependent X-ray photoelectron spectroscopy (XPS) and thermal desorption spectrometry (TDS) have been used to study the room-temperature adsorption and thermal evolution of ethanolamine. Like allylamine, the presence of a broad N 1s feature at 399.1 eV commonly attributed to N–Si indicates N–H dissociative adsorption of ethanolamine, while the O 1s feature at 533.1 eV indicates the formation of Si–O bond and O–H dissociation as found in allyl alcohol. Furthermore, a broad C 1s envelope, corresponding to the C–N feature at 284.9 eV and C–O feature at 285.7 eV, is observed. These XPS data are consistent with the [N, O] bidentate staggered and eclipsed ethanolamine conformer adspecies resulting from N–H dissociation and O–H dissociation, as predicted by our Density Functional Theory (DFT) calculations. The adspecies remains stable upon annealing to 595 K, above which C–N and C–O dissociation occurs, as reflected by the conversion of existing XPS features to a new N 1s feature at 397.7 eV corresponding to Si–N(H)–Si and a new O 1s feature at 532.0 eV corresponding to Si–O–Si, with no loss in the respective total intensities up to 1190 K and 1090 K, respectively. The spectral evolution of the N 1s and O 1s features is also consistent with the emergence of a new C 1s envelop near 285.3 eV, corresponding to the dissociated →C–C← (ethanyl) adspecies, at 595 K. The minor loss (30%) in the total C 1s intensity and the emergence of TDS features of m/z 26, 27, and 28 near 615 K further support that some of the ethanyl adspecies has desorbed as ethylene. The majority of the ethanyl adspecies is found to remain on the surface and is converted at 890 K to SiC, with representative C 1s feature at 283.2 eV. The observed thermal evolution suggests the possibility of thermally controlling the conversion of a double NH and O passivated Si(100) surface at 595 K to a N passivated Si(100) surface at 1190 K. Unlike the multidentate allyl alcohol and allylamine adspecies that are found to be not favoured kinetically, the formation of the present [N, O] bidentate ethanolamine adspecies appears to be kinetically favoured on Si(100)2×1.
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Document Type: Research Article
Publication date: June 1, 2011
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